X-ray tube



y 1941- A. MUTISCHELLER 2,250,963 I X-RAY IUBE Filed Nov. 21,. 1939 INVEN T0 R.

Patented July 29, 1941 UNITED STATS ar rr cE This invention is for an improved X-ray tube of the hot cathode type having many valuable features and advantages over the old types of X-ray tubes. This present application is a con tinuation in part of my application filed Dec. 10, 1937, Serial No. 179,094 for Discharge tube, now Patent No. 2,216,209.

' More specifically stated, the allowable power through a hot cathode type X-ray tube is generally that which, due tothe discharge, causes the focal spot on the anode to become hot, and ultimately incandescent. As soon as this condition arises, the anode also emits electrons and the formerly unilaterally conducting tube becomes then bilaterally conducting] The result is then that the tube generallyis damaged and that the energy passing through it is no longer controllable with the temperature of thehot cathode.

To avoid damage to the tube, a'rectif er device of one kind or another is required if the energy transmitted through the tube exceeds the amount which causes heating in thesense mentioned above of the anode focal spot. These rectifiers are costly, troublesome, bulky and requiring adjustment and attention. Furthermore, when the X-ray tube blocks every second reversely poled impulse and allows only the correctlypoled impulses to pass, then the blocked impulses generally erect a higher voltage'due to the ohmic and other losses of voltage of the impulses that pass through the tube. Thus, if a large amount of energy is allowed to pass through the X-ray tube, then the voltage losses of the passing impulses are relatively large in comparison with the no-current normal transformer voltage of the blocked impulses. This causes an abnormally high inverse voltage over the X-ray'producing voltage of the impulses passing through the tube, and therefore it requires higher insulation than that required for the X-rayproducing voltage and also this results in a power factor which is about one-half that of the fully rectified current resulting from the use of a full-cycle rectifier.

Through my invention the requirement for rectifiers is avoided for with it the alternating current applied to the X-ray tube is rectified within the envelope of the tube and thus any of the disadvantages of rectifiers in air are eliminated. The result is, that this X-ray tube can be directly connected to an alternating current source and it can be operated with much larger energy than that possible with blocking of inverse impulses; it has no higher inverse voltage, it is for that reason easier toinsulate and less strenuous on insulated cables and insulators; the

requirements of power feeder capacity is about one-half that required for the impulse blocking type of X-ray tube.

In the aforementioned co-pending application the means and the method are described and disclosed by which it'is possible toprevent the shortcircuiting of electrons from one of the inlet electrodes and terminals directly 'over to the other without-following, the prescribed and intended path; 'In this'divisional application, these methods. of accomplishing this are more specifically applied to function in an X-ray tube.

In Fig. l is shown, diagrammatically, how with the aid of a diaphragm of insulating material and with operating some cooperating electrodes at saturation and other cooperating electrodes below saturation, the electron discharges from both the positive and the negative half-cycles I can be focused upon one anode.

In Fig. 2 is shown, diagrammatically, how an escape of electrons to the outside of these cooperating anodes and to any other electrode is prevented.

In Fig. 4 is shown how the X-ray tube illustrated in Fig. 2 can also be energized through a single cable from one end of a grounded transformer.

I 'In Fig. 1 are shown, in diagrammatic form, two

ways of preventing the undesired passing, of electrons or of short-circuiting directly from one of a pair of cooperating electrodes to one of another pair of cooperating electrodes. One way is to place the cathodes of the inlet terminals in one compartment and the anodes in another compartment. The division between or separation of the. compartments consists of dielectric material such as a septum of glass, porcelain, mica or other dielectric, material. In this example, the anodes3l and 36 "are on one side of the partition wall 39 and are therefore in the compartment 38; the cathodes 34 and 35 are on theother side of it and in compartment 29. Therefore, a direct 'discharge from cathode 35 to anode 3|, or from cathode 34 to anode 36 are prevented and the discharge must take place between cathode 35 and anode 33 and then between cathode 32 and anode 3| or from cathode 34 to anode 33 and from cathode 32 to anode 36.,

Thus the current flowing from the anode 33 to the cathode 32 is then unidirectional.

Another way is to operate the discharge from the cathode 34 to the anode 33 or from the cathode 35 to the anode 33 at voltage saturation and the discharge from cathode 32 to anode 3| or from the cathode 32 to the anode 36 below saturation; or so that the emission of electrons from the cathode 32 is larger than that from the cathode 34 or 35 and in particular when the voltage applied between the cathodes 34 and 35 and the anode 33 is sufficient to drive all the electrons emitted by these cathodes over to the anode.

In Fig. 2 a third way is shown diagrammatically how the undesired passage of electrons between non-cooperating electrodes can be prevented. A pair of anodes of special design are 42 and these are hollow and partly surrounding the cooperating cathode 48 and 49 so that, even if operated below voltage saturation, the voltage applied between other cooperating electrodes can not force electrons out from one of these hollow anodes. But, in addition, the cathodes 46 and 43 areprovided with focusing shields 63 and 64 so shaped and placed that they direct the electron dischargeuponthe area 41 of the anode which is an X-ray anode. The portion 41 is usually of tungstenand the part 55 surrounding it is of copper. When the terminals 44 and 4| are energized with high voltage alternating current,

and at the moment 44 is negative, then electrons will be emitted'from the cathode 46; these will be accelerated by the potential applied which must be sufiicient to cause voltage saturation and the electrons from cathode 46 will be focussed upon and received by the anode 55. Being thus accelerated, the electrons are not attracted to the cathode 43, which at this moment is positive, but the electrons possesssuificient kinetic energy not to be deviated from their normal path.

Although the path of the electrons seems to be fully controlled, it often happens that the X-ray tube is not always operated at full saturation or that there may be reflection of electrons from the anode; it ishighly useful to surround the cathodes 48 and 49 with hollow anodes such as those at 42 and 45, to prevent any excess of electrons over those discharged between the X-ray producing electrodes from reaching out into the evacuated space within the envelope. The function of the hollow anodes 42 and 45 is therefore in addition to the operating at saturation and out of a focussing shield of the cathode 46; both these functions are to prevent electrons from reaching, for example, from cathode 46 to cathode 43 or to anode 42, or from cathode 43 to cathode 46" and anode 45.

Therefore, the path of electrons, if we assume the'terminal- 44 to be negative, is as follows: from terminal 44 along conductor 56 to cathode 43; from there to focal spot 4T of anode 55; from anode 55 through the milliampere meter 5| to the cathode 49; from there to anode 42 along conductor 59 and out through terminal 4|. If the terminal -4| is negative, then the path of electrons is as follows: terminal 4| along conductor 58 over cathode 43, to focal spot 41 of anode 55, through the meter 51 to the cathode 48; from there to anode 45 along conductor 51 and out to terminal 44. In this case the cathodes 46 and 43- are operated at voltage saturation and the cathodes 48 and 49 below voltage saturation.

This same device can also be operated as follows-: if terminal 44 is negative, the electron flow is from terminal 44 along conductor 56 to cathode 46; from there to focal spot 41 on the anode 55; from anode 55 through the milliamperemeter 5| to the cathode 48; from there out through the leads 6| and 62. If the lead wires 6| and 62 are negative, the electron flow is, from terminal wires 6| and 62 to cathode 48; from there over to anode 45 along conductor 51 out through terminal lead wire 44. In this case, the cathodes 43 and 49 and the anode 42 are not utilized.

Still another manner in which the same device can be operated is illustrated diagrammatically in Fig. 4. If terminal 4| is connected to one terminal of a transformer having its second terminal grounded and this terminal is negative,

- then the electrons pass along conductor 58 to cathode 43 to the target 41 and anode 55; from there they pass through the meter 5| to cathode 48 over to anode 45, along conductor 56 to cathode 46. If this cathode 46 is operated at saturation and cathodes 43 and 48 below saturation, then a negative charge will pile up on these parts due. to the capacityofj' the parts: anode 45 leads 51,44 and 56 and cathode 46, especially if in addition a condenser is connected with one electrode to terminal 44 while its other electrode is grounded; If terminal 4| is positive, then electrons are drawn from cathode 49 to anode 42 and a positive charge will pile up on theparts: anode 55, meter 5|, and cathode 49, especially if inadditionacondenser having its second electrode' grounded is connected to terminal 62. Thus the negative charge piled up on the parts: cathode 46, conductors 56, 44 and 51 and anode 45, will discharge from cathode 46 over to anode 55 and focal spot 41:170. neutralize the positive charge piled up on the parts: anode 55, meter 5|, cathodes 48 and 49 and leads 6| and 62. X-raysv are then produced by the impact of the electrons. which were accelerated between the cathode 46 and the focal'spot 41 of the anode 55.

The construction of a hollow anode together with a cooperating cathode, such as those indicated in Fig. 2, is shown'more in detail in Fig. 3. The hollow anode '96 is supported on a stem 9|- andit. has an opening with rounded edges 92 which 'is generally smaller in diameter than the diameter of the hollow anode. The cathode 96 maybe a fiat spiral, loops or mushroom-shaped coils,-but'the loops or coils should be substantially equidistant from the anode wall. The cathode is supported on stout lead-in wires 93 and 94. There may be mounted, without producing shortcircuiting between the leads 93 and 34-, near the opening of the anode 99, a disc of conductive material whose purpose is to shield the opening in the anode and to prevent the escape of electronsfrom the inside of the anode. In this way an electrostaticfield can be set up which prevents the escape of electrons from the inside of the hollow shell or anode.

The foregoing description refers to operation of the X-ray tube with single phase alternating current. In the light of the preceding it is however, easy for a person skilled in this art to provide a multiple of sets of inlet electrodes and then-this novel X-ray tube can be operated and energized with multi-phase alternating current.

Having thus,.in order to describe my invention, described and illustrated several specific types of apparatus embodying the principle thereof, I herewith state, that these are not all the possible ways and manners in which the invention can be carried out. The following claims are to cover all other possible variations which any person skilled in the art may suggest and devise as equivalents in so far as they are not the result of any additional inventing on his part.

I claim:

1. An X-ray tube comprising an envelope having therein an X-ray anode having refractory portions for receiving electrons at voltage satu-' ration, and a thermionic cathode having electron emitting sections, an auxiliary hollow anode substantially enclosing each of said electron emitting sections, additional thermionic cathodes adjacent said X-ray anode and each having a focusing device to direct the discharge therefrom upon the refractory portion of said X-ray anode, independent leads connected to said first mentioned cathode and to each of said additional thermionic cathodes, a conductive connection between said X-ray anode and said first mentioned cathode and between each auxiliary anode and one only of said additional thermionic cathodes. 2; An X-ray tube comprising an envelope having therein an X-ray anode having a section for receiving electrons at voltage saturation, and a cathode having electron emitting sections, an additional anode adjacent each of said electron emitting sections, additional thermionic oathodes adjacent to said X-ray anode, a focusing shield about each of said additional thermionic cathodes to direct the electron discharge therefrom upon the electron receiving section of said X-ray anode, independent leads connected to said first mentioned cathode and to each of said additional thermionic cathodes, a conductive lead between said X-ray anode and said first mentioned cathode and a conductive connection between each additional anode and one only of said additional thermionic cathodes.

3. An X-ray tube comprising an envelope having therein an anode for producing X-rays and a thermionic cathode having double electron emitting sections, two additional anodes one adjacent each of said electron emitting sections, two additional thermionic cathodes adjacent said X-ray producing anode, independent leads connected to said double section cathode and to each of said additional thermionic cathodes, a lead connecting said X-ray producing anode and said double section cathode together and conductive connections between each additional anode and one only of said additional thermionic cathodes, and a partition of dielectric material between the non-adjacent electrodes as a shield against electron discharges between non-adjacent electrodes.

4. An X-ray tube comprising an envelope having therein an anode for producing X-rays and 'a thermionic cathode having electron emitting sections, an additional electron receiving anode adjacent each of said electron emitting sections, additional thermionic cathodes, a focusing shield about each of said additional thermionic cathodes for directing the electron discharge therefrom upon said main X-ray anode, independent leads connected to said first-mentioned cathode and to each of said thermionic cathodes, a lead connecting said first-mentioned cathode and said main X-ray anode together and a conductive connection between each additional anode and one only of said additional thermionic cathodes.

5. An X-ray tube comprising an envelope having therein an X-ray anode and a thermionic cathode having electron emitting sections, an additional anode adjacent each of said electron emitting sections, additional thermionic cathodes adjacent said main X-ray anode and having a means for focusing the discharge therefrom upon said X-ray anode, independent leads connected to said first-mentioned and to each of said additional thermionic cathodes, a lead connected tosaid main X-ray anode, to a measuring device and to said first mentioned thermionic cathode, a conductive connection between each additional anode-and one only of said additional thermionic cathodes, and means for preventing electronic discharges between said additional cathodes and said additional anodes.

6. An X-ray tube comprising an envelope having therein an X-ray anode having refractory portions for receiving electrons at voltage saturation, and a thermionic cathode having double electron emitting sections, two additional hollow anodes each substantially enclosing one of said electron emitting sections, two additional thermionic cathodes adjacent said X-ray anode and each having a focusing device to direct the discharge therefrom upon the refractory portion of said X-ray anode, independent leads connected to said double section cathode and to each of said two additional cathodes, a conductive connection between said X-ray anode and said double section cathode and between each additional anode and one of said additional thermionic cathodes.

7. An X-ray tube comprising an envelope having therein an X-ray anode with sections for receiving electrons at voltage saturation, and a cathode having two electron emitting sections, an additional anode adjacent each of said two electron emitting sections, twoadditional thermionic cathodes adjacent to said X-ray anode, a focusing shield about each of said two additional thermionic cathodes to direct the electron discharge therefrom upon the electron receiving section of said X-ray anode, independent leads connected to said first mentioned cathode and to each of said two additional cathodes, a conductive lead between said X-ray anode and said first mentioned cathode and a conductive connection between each additional anode and one of said additional thermionic cathodes.

8. 'An X-ray tube comprising an evacuated envelope having therein an anode for producing X-rays and a thermionic cathode having two electron emitting sections, an additional electron receiving anode adjacent each of said two electron emitting sections, two additional thermionic cathodes, a focusing shield about each of them for directing the electron discharge therefrom upon said X-ray anode, independent leads connected to said first mentioned cathode and to each of said additional cathodes, a lead connecting said first mentioned cathode and said X-ray anode together and a conductive connection between each additional anode and one of said additional thermionic cathodes.

9. An X-ray tube comprising an evacuated envelope having therein an X-ray anode and a thermionic cathode having two electron emitting sections, an additional anode adjacent each of said electron emitting sections, two additional thermionic cathodes adjacent said X-ray anode and each having a focusing means for focusing the discharge therefrom upon said X-ray anode, independent leads connected to said first mentioned cathode and to each of said additional cathodes, a lead connected to said X-ray anode, to a measuring device and to said thermionic cathode having electron emitting sections, a conductive connection between each additional anode and one of said additional thermionic cathodes, and means for preventing electronic discharges between said additional cathodes and said additional anodes.

10. An X-ray tube comprising a highly evacuated envelope having therein insulatively mounted and with terminals to the outside an X-ray anode and a thermionic X-r-ay cathode adjacent to and cooperating with each other and said cathode having means for focusing the electron discharge therefromuponsaidX-ray anode,an additional anode and an additional cathode cooperating with each other, means conductive for electron passage from said X-ray anode to said additional cathode and from said additional anode to said X-ray cathode, independent leads insulatively mounted and leading to terminals outside said envelope connected to each cathode, and means to prevent the passage of electrons between non-cooperating electrodes.

11. An X-ray tube comprising a highly evacuated envelope having therein insulatively mounted an X-ray anode and a thermionic X-ray cathode adjacent to and cooperating with each other and having terminals to the outside of said envelope and said cathode having means for focusing the electron discharge therefrom upon said X-ray anode, at least one additional anode and one additional cathode cooperating with each other, electron conductive means connecting from said X-ray anode to said additional cathode and from said additional anode to said X-ray cathode, leads insulatively mounted and leading to terminals outside said envelope connected to each cathode, and means for preventing the passage of electrons between non-cooperating electrodes.

12. An X-ray tube comprising a highly evacuated envelope having therein insulatively mounted an X-ray anode and a thermionic X-ray cathode adjacent to and cooperating with each other and having terminals to the outside of said envelope and said cathode having means for focusing the electron discharge therefrom upon said X-ray anode, at least two additional sets of discharge electrodes each set having an anode and a cathode adjacent to and cooperating with each other, means conductive for the passage of electrons from said X-ray anode to the cathode of one of said sets and from the anode of said set to the cathode of the second set and from the anode of said second set to the said X-ray cathode, insulated leads leading to terminals outside said envelope connected to each of said cathodes and means for preventing the passage of electrons between non-cooperating electrodes.

ARTHUR MUTSCI-IELIHJR. 

